Issue 45

L.M. Viespoli et alii, Frattura ed Integrità Strutturale, 45 (2018) 121-134; DOI: 10.3221/IGF-ESIS.45.10 128 where:       m ref ref MPa N cycles m 6 71 ; 2 10 ; 3 Applied Load Nominal Stress Expected Fatigue Life Specimen N° Cycles at Failure kN MPa Cycles 75 160 174761 1 235053 2 295488 65 140 260868 3 493451 4 369923 85 180 122740 5 154924 6 189280 Table 2 : Nominal Stress Approach results summary and comparison with experimental results. S TRUCTURAL H OT S POT S TRESS A PPROACH he Structural Hot Spot Stress [2,24-25] is individuated by extrapolation from the nodes (Fig. 2) at the reference points to the hot spot. Depending on whether two or three reference points are used, the extrapolation can be linear or quadratic. Moreover, depending on the stress gradient towards the weld toe, a fine mesh of linear elements or a coarse mesh of quadratic mesh can be adopted. The hot spot in question is of the type “a”, that is, weld toe on the plate surface and all the three different discretization configurations introduced for the type are used in the study to compare the results. As reported in the IIW document, page 78, the class for steels for a longitudinal attachment of length inferior to 100 mm, with fillet weld in as welded conditions, is FAT 100. The model has been discretized with the SHELL181 element, which is a linear, four-node element with six degrees of freedom at each node. The structural hot spot stress for linear extrapolation can be computed as:      hs t t 0.4 1.0 1.67 0.67 The predicted fatigue life results to be:       m m ref ref N N N 0 where:           m hs ref ref MPa N cycles m 6 0 ; 100 ; 2 10 ; 3 Applied Load Nominal Stress Structural Hot Spot Stress Expected Fatigue Life Specimen N° Cycles at Failure kN MPa MPa Cycles 75 160 186 310807 1 235053 2 295488 65 140 163 461814 3 493451 4 369923 85 180 209 219074 5 154924 6 189280 Table 3 : Structural Hot Spot Stress Approach results summary and comparison with experimental results. T